IRS Assist Wireless communication: Scenarios, Advantages, Convergence

: Intelligent Reflective Surfaces (IRS), as a passive, low-cost, and green technology, are widely considered to address the high complexity, high hardware costs, and increased power consumption pressures faced by future wireless networks to provide large-scale connectivity services to a larger number of devices around the world. This paper summarizes the advantages of IRS technology compared with other technologies, and demonstrates the effectiveness of IRS assisted wireless communication technology in new scenarios combined with related technologies. In particular, for IRS assisted relay scenario, the feasibility of this scheme to improve the physical layer security of the system is discussed in detail

phase shift of reflected signals to change the wireless propagation environment by using low-cost passive components based on a time-varying environment, resulting in high passive beamforming gains. Because IRS operates in full duplex mode and requires low power consumption, it is a candidate solution to improve energy and spectrum efficiency. Compared with traditional technologies such as active beamforming and relaying based on large-scale multiple input and multiple output (MIMO), IRS eliminates signal amplification and regeneration, resulting in lower hardware costs, energy consumption, and interference pollution. Also, IRS has effective short-range/local coverage that can be deployed intensively at a scalable cost, but does not require complex interference management as long as they are sufficiently separated from each other, in addition to IRSassisted wireless communication technologies that have the advantage of being easy to deploy and sustainable to operate, IRS can be easily integrated into communications environments because of their very small hardware footprint, not only can it be easily and flexibly deployed in the exterior wall and interior of the building, but also can be embedded in the ceiling, furniture, computer cases, even clothes and other surfaces, which provides a high degree of flexibility and excellent compatibility for wireless communication and does not consume extra energy, so it has a broad application prospect in the future wireless communication network .
With the further development of the research, the application of IRS assisted wireless network in different scenarios and different technologies keeps emerging, and the transmission performance of the system is further improved by combining with other technologies. Based on this, this article considers IRS-assisted mobile communication and summarizes it.

IRS versus other communication technologies
IRS has the following advantages over existing related technologies, namely conventional reflective surfaces, AF relays, active intelligence surfaces, backscatter communications, and massive MIMO.
First, thanks to recent breakthroughs in Microelectromechanical Systems and composites, IRS can reconfigure reflection coefficients in real time, whereas traditional reflective surfaces only have fixed reflection coefficients.
Second, IRS is a green and energy efficient technology that passively reflects incoming signals without additional energy consumption, whereas AF relays and active intelligence surfaces require active RF components. Active AF relays typically operate in half duplex mode and are therefore less spectral efficient than IRS operating in full duplex mode. Although AF relaying can also work in full duplex, it is inevitably subject to severe self-jamming, which requires effective jamming cancellation techniques.
Third, although both IRS and backscatter communications use passive communication, IRS can be equipped with a large number of reflecting elements due to complexity and cost limitations, whereas backscatter devices are usually equipped with single/few antennas.
Fourth, IRS only attempts to assist the intended transmission of signals between transmitter and receiver pairs, enhancing the performance of the existing communication link, and not its own information transmission, whereas traditional radio frequency identification devices tag backscatter communication (communication with the receiver by reflecting the signal sent from the reader) needs to support the transmission of information from the backscatter device. Thus, the direct path signal in backscatter communication (from reader to receiver) is an unwanted interference that needs to be eliminated/suppressed at the receiver. However, in IRS enhanced communication, both direct path and reflected path signals carry the same useful information and can therefore be added coherently at the receiver to maximize the total received power.
Fifth, massive MIMO uses large antenna arrays to improve spectrum and power utilization, which is more dependent on the utilization of each RF chain and powerful signal processing algorithms. Literature for the first time analyzed the capacity of IRS, demonstrating that the capacity per square meter of IRS is linear with the average transmission power, while the large-scale MIMO is logarithmic. In addition, IRS differs from massive MIMO based on active intelligence surfaces due to different array architectures (passive versus active) and operational mechanisms (reflection versus emission).
Sixth, other communication technologies, such as mmwave communication, intensive networking, etc., these related technologies cannot control the wireless transmission environment and energy consumption.

IRS combines with other communication technologies
As shown in Table 2, applications of IRS-assisted wireless networks in different scenarios and technologies are emerging.

IRS assists relay
In this section, taking IRS assisted relay communication as an example, the advantages of this scenario and the significant features of improving physical layer security are elaborated in detail.

IRS combines with traditional relay
Considering the fact that the previous generations of mobile communication technologies have deployed a large number of relays in the actual communication environment, combined with the advantages provided by IRS to overcome the current communication challenges, this paper considers to integrate the two technologies, and proposes a widely deployed relays and IRS communication model, so as to provide more efficient, stable and reliable communication services for target users.
In terms of network architecture, compared with the traditional single-link network, the relay collaborative IRS communication network can effectively meet the network demand of the rapid growth of data traffic and user traffic, enhance the expected signal strength of the receiving node, reduce the wireless network access cost, effectively utilize the relay resources, expand the communication coverage, reduce the system power consumption, improve the system capacity and security performance. In line with the new development trend of future mobile communication, it can provide services for new application communication such as IoT, IOV, smart city and smart home in future mobile communication.
With the rapid deployment of relay collaborative IRS system, although the network architecture is heterogeneous and complex, its network coverage, data rate and network capacity are also improved.
To be specific, firstly, Alleviates the communication interruption caused by the small wireless coverage area of BS communication, limited BS resources and energy consumption, deployment in remote areas, or difficult battery replacement of equipment.
Secondly, it can strengthen the communication quality of users and the coverage range of indoor communication. In particular, for the scene where line of sight is blocked and the communication is blocked, a new type of non-line-of-sight link with good performance can be created to assist the communication. Specifically, in specific cases, the communication quality of densely populated cities can be expanded.
Third, for users on the edge of the cell, improve their communication quality, eliminate inter-cell interference, reduce the average load of single BS, reduce the average congestion of network capacity, and improve the data transmission rate of the network. Its passive, intelligent and passive characteristics improve the quality of the communication environment and improve the dynamic network capacity adjusted on demand. It also provides the possibility for further optimizing network security and enhancing anti-interference capability.
Fourth, rich relay nodes assist IRS communications, improve end-user service quality, and enhance security performance.
Fifth, by configuring different wireless technologies such as transmission power, antenna number, number of relays and coverage area, the system performance can be improved and personalized services can be provided to the vast number of users. Figure 1. Relay cooperation IRS network architecture As shown in Figure 1, the IRS system framework of relay collaboration is given. However, for any end user, it is very important to improve the quality of service and ensure safe transmission. Therefore, the development of the IRS network of relay collaboration is still mainly focused on the secure transmission of user information.

IRS assists physical layer security
The essence of wireless physical layer security, that is, the intrinsic security of wireless channel is utilized by physical layer. It is a technology that utilizes the intrinsic characteristics of wireless channel and noise to realize the safe transmission of wireless signal. By taking advantage of the diversity and time-variability of wireless channel as well as the uniqueness and reciprocity of both channels of legitimate communication, it starts from the objective law of wireless signal transmission. Mining the internal security elements of wireless channel. These security elements are naturally parasitic in the communication process and signal processing technology, which can evolve and integrate with the new air interface technology to promote the integration of security and communication. Different from the traditional security means that rely on key encryption, it is an endogenous security mechanism and manifestation of physical layer wireless communication. From the perspective of information theory, physical layer security provides another way to deal with the problem of communication security.
The traditional network optimization in wireless communication system is limited to the transmission control at the transceiver, but pays little attention to the wireless communication environment. This is mainly because the wireless propagation environment has long been regarded as an entity of uncontrollable and random behavior between transceivers. In addition to being uncontrollable, the environment usually adversely affects communication efficiency due to the introduced signal attenuation, fading, and interference. As a result, the propagation environment itself becomes the main limiting factor which hinders the further improvement of wireless network performance. Recently, there has been an increasing demand for new communication paradigms that can intelligently adjust the communication environment to improve communication efficiency or simplify transceiver architectures. In this regard, the IRS has received a great deal of attention for its ability to reconfigure the propagation environment through softwarecontrolled reflection, so the IRS assists the physical layer secure communication model to reconfigure the wireless propagation environment to facilitate transmission to meet the new challenges posed by increasing performance requirements.
As shown in the figure 2, the transmission of the legitimate link is enhanced by optimizing the passive beamforming vector at IRS, and the signal reception of the listening link is offset, thus improving the security performance of the wireless network.

Conclusion
With the explosion of wireless network data volume, how to achieve the balance between performance and energy efficiency in the next generation of mobile communication is a major challenge. This paper investigates one of the candidate technologies, IRS, respectively summarizes the advantages of IRS technology compared with other related technologies and the new scenarios of combining with other technologies. In particular, The IRS assisted relay communication technology is described in detail. This article envisages that IRS technology will be widely used in the future to solve resource-constrained wireless transmission.